Now I see things as they truly are...

Welcome to my guide for King Leoric the Laning King!
In this guide, I will explain my idea on how Leoric can be played.

The key talent of this build is Fealty Unto Death. This talent empowers Leoric's lane presence exponentially, allowing him to dominate the lane. Other talents will supplement your lane control, allowing you to push/defend and slaughter!...uhh, defeat foolish heroes that stand in your way.

Note that the spotlight is quite old but it's still a great guide. Not much was changed about the Skeleton King: Undying now also improves Leoric's basic attacks and some talents have been moved/changed.

LEVEL 1

..... As I already mentioned, this is the heart of the build. Although the other two talents are solid choices for sustain, in my opinion, this one is the best bang-for-the-buck (FOR THE PURPOSE OF THIS BUILD, in other scenarios/builds the other two talents are far better and more viable). There is a catch for other two talents: Consume Vitality requires you to hit an enemy hero, while Ossein Renewal has a cooldown (it can be reduced but still while on CD you won't heal). Fealty Unto Death only requires you to be near Minions that die, both ENEMY and FRIENDLY Minions! So it is constantly active and it restores HP in % (great for scaling obviously) and also adds some flat MP as well. You will NEVER defeat me!. All of these benefits for a Level 1 talent! It's too good to miss.

LEVEL 4

..... This one goes well with the previous talent. Faster lane clear is good in general, but with Fealty Unto Death it is even better. In the end, the goal is to destroy the enemy Nexus however possible. Greater lane clear results in a faster push (duh!). Kneel, Peasants! is a great tool for lane control because it affects Mercenaries as well. Add in the Auto Attack cleave from Undying and all shall suffer as I have suffered!... yeah, you get the point.

LEVEL 7

..... For this tier you can also go for the other two, although I consider this one to have a slight edge over Drain Momentum and Hopelessness. Since Drain Momentum removes Leorics movement speed slow and Hopelessness adds extra range, it is much easier for Drain Hope to last its full duration. Willing Vessel will reward you with extra healing over its duration (full duration or otherwise), but it lacks utility that the other two talents have. I'd go for this one non the less. This tier is quite a selec--A masterful selection!, but you can pick something else if the situation requires you to.

LEVEL 10

..... More viable than March of the Black King. It can be used as intended to trap somebody or just block an enemy hero trying to engage and so on. Heroes such as Tracer, Fenix, Genji can escape the tomb with ease. The same applies to March of the Black King. If you have a hero, such as Tassadar, on your team with Force Wall, it may be more beneficial to go for the march instead. So either provide some CC with Entomb or go for raw damage with March of the Black King. In most cases, I would go for Entomb even if the team is doing fine with CC, because it never hurts to add some more!
Although I never quite understood why it is march of the BLACK king and not march of the SKELETON king. Doesn't make much sense. I prefer the black king. It is much more... ominous. Well Leo it still makes no sen-- DO NOT SPEAK TO ME IN THOSE TONES! Okay, let's move on...

LEVEL 13

..... This goes really well with Willing Vessel. Combined, it will result in more healing and more damage. Much like Willing Vessel it will reward you with an EXTRA effect if you manage to keep Drain Hope up for the entirety of its duration. The math behind this talent is that if Drain Hope lasts for all 4 seconds, than you will reduce it's CD from 10 to 6 seconds. NOTE! that the CD starts as soon as Drain Hope is used - meaning that Unyielding Despair will accelerate the CD exponentially.
I'd also consider picking hardened bones if I am dealing with a heavy physical damage team.

LEVEL 16

..... Quite straight forward talent. You get more attack speed. Kill more stuff and get even more attack speed. That additional attack speed can be acquired easy due to the fact that Leoric himself won't have to last hit minions or heroes. Not much to add about this talent really. More attack speed adds to more damage done.
In this tier I would also consider Crushing Hope. If the enemy team is heavy on tanks/bruisers or just a lot of high health heroes, this talent is a great choice. Although, generally speaking, 15% is a lot of damage regardless of the health pool size. But it does require you to keep Drain Hope up for the entirety of its duration (usually easier said than done).
Royal Focus isn't a viable choice for THIS build. This talent is great if you are going to engage, but you should have Consume Vitality and Paralyzing Rage or Ghastly Reach if you are planning to dive head on into enemy forces.

LEVEL 20

..... In my opinion everything here is more or less viable (excluding Death March for it is too unpredictable, other options are way better and safer). However in order for Leoric to become a true Laning King, you should spec into Burning Despair. This is also a rare buff that actually doesn't require you to use Drain Hope nor for it to last its full duration. If you do and the longer Drain Hope lasts - you will get more out of Burning Despair.
My 2nd option here would be Spectral Leech. It goes really well with Mithril Mace. Again, this is really good against higher health heroes. The healing you will get from it is notable and it will give Leoric an upper hand in most fights.
A more defensive pick, but non the less effective, is Shroud of the Dead King. This is GOD MODE for 3 seconds (God King Leoric skin - coincidence ?!). Good if you need to soak tons of damage that would otherwise kill anything living or undead in the Nexus!
As for the heroic upgrade: Buried Alive is mainly chosen for its silence, which is good against heroes that can jump out of Entomb.

Let's get one thing straight right away: Building Leoric this way doesn't mean you should hug your lane tight and never ever let go! Your responsibility as a Warrior is much greater. This build allows you to dominate the lane and although some talents (such as March of the Black King, Ominous Wraith and Royal Focus) that are suited for (team)fight initiation are skipped in favor of lane clearance, you still have to have yourself on the front lines smashing heads with your hammer!
Talents alone DON'T define the gameplay. I already mentioned what talents can be moved around to suit individual preferences or situations. In this segment, I will explain how to work with the talents you got.
The following applies to all maps - alternatives can be made when/if necessary.

Level 1 - Level 4

This is the period before the first event of the map starts. Your primary objective will be to clear the lane and soak exp. Obviously, go for the kill if the opportunity presents itself. Fealty Unto Death will keep you sustained (not as much as a healer would but it's still better than regeneration globe or passive health regeneration). It also restores FLAT MANA so you can spam Skeletal Swing, especially once you get Kneel, Peasants!. Make sure you are sustained and prepared for the objective to come.

Level 4 - Level 7

So the objective was done and everybody goes back to what they did before. This applies to you too. Once you reach Level 7 and obtain Willing Vessel trading with enemy heroes will be much more effective. Nobody likes to stand in Drain Hope range. With this talent they will be even more reluctant. With this new-found power proceed as you did on previous levels.

Level 7 - Level 10

Around this time there will be another objective. This is the heroic ability race since they offer a massive damage spike. Obviously you will want to hit 10 before the enemy team and pummel them to the ground! Both teams will struggle hard to beat the other to level 10 first. Contribute to this as much as possible by primary staying alive - a dead man doesn't gather exp.

Level 10 - Level 13

Once you get your heroic, now you will spend more time with the team. Now you will be focused on soaking more damage, rather than exp. Unyielding Despair will allow you to Drain Hope more often and keep you sustained in fights as muc has possible. When you are not fighting, pressure lanes as much as you can.

Level 13 - Level 16

It is crucial to lane after team fights/skirmishes. Find whatever way possible: you will need it so you may get Mithril Mace. This talent is a massive auto attack buffer and that will benefit you whomever you fight. So make sure it is obtained and empowered A.S.A.P.

Level 16 - Level 20

Considering you go for the Burning Despair, it will allow you to become a one man army. Dealing with massive Minion waves, Mercenary pushes/camps and most objectives (such as the one on Infernal Shrines) will be quite easy. Even if you go for Shroud of the Dead King, Buried Alive, etc. you will still be able to do everything mentioned. As I said, don't let that carry you away too much, you are still a Warrior and you have a job to do.

Lastly, I just want to mention that nothing is set in stone 100%. Make adjustimants as needed, good luck and enjoy playing Leoric the Lan--WHAT?! - the Skeleton King!

Note: For those who didn't figure it out, red text is Leoric speaking (it is a joke on his everlasting presence with Undying).